Wireless communication systems allow wireless devices to communicate without the necessity of wired connections. Because wireless systems have become so integrated into daily life, there is a growing demand for wireless communication systems that support multimedia services such as speech, audio, video, file and web downloading, and the like. Various wireless communication protocols and transmission control mechanisms have been developed to meet the growing demands of multimedia services over wireless communication networks and to improve the performance of these multimedia services.
An exemplary transmission control mechanism for transmitting packet data units (PDUs) in wireless communication systems is Hybrid Automatic Repeat Request (HARQ). Using HARQ, the devices of a wireless system (e.g., transmitting devices, receiving devices, relay devices, etc.) may be configured to retransmit PDUs when the PDU is either not received by the intended recipient or received with errors. Generally, there are two main variants of HARQ retransmission mechanisms supported in wireless communication systems: incremental redundancy (IR) and chase combining. Using IR, a physical (PHY) layer will encode the HARQ packet to generate several versions of encoded subpackets, called redundancy versions. In IR, the encoding process may include the steps of encoding, interleaving, and puncturing, and multiple redundancy versions may be created when the HARQ packet passes through these steps. For chase combining, the PHY layer also encodes the HARQ packet. However, only one version of the encoded packet is generated. Thus, in chase combining, the transmitting device retransmits the same encoded version every time retransmission is required.
Generally, one factor impacting channel quality is the distance between the transmitting device and the receiving device, such as when a receiving device is located near a boundary of a wireless communication cell. Different levels of modulation and coding schemes (MCSs) may be used based on known transmission and/or channel quality information so that more robust MCSs may be used to increase the likelihood that the PDU may successfully be received and decoded by a receiving device. As a result, receiving devices closer to a transmitting device may have better channel quality and be able to successfully decode PDUs using a less robust MCS, whereas receiving devices that are at a greater distance from the transmitting device may have poorer channel quality and will only be able to successfully decode PDUs using a more robust MCS.
When performing point-to-point (PTP) transmissions of PDUs (i.e., from a transmitting device to a single receiving device), a transmitting device may modulate and code a transmission packet for a single receiving device based on channel quality information reported from the single receiving device. However, when performing point-to-multipoint (PTM) transmissions of PDUs (i.e., from a transmitting device to multiple receiving devices), each of the receiving devices may have different downlink channel conditions, and the transmitting device may need to adopt the most robust modulation and coding schemes for transmission to all the receiving devices.
In order to provide every receiving device with an opportunity to correctly receive and decode the packet data, the transmitting device may adopt the most robust MCS capable of successfully transmitting packet data to every member of the group of receiving devices. To do so, the transmitting device may evaluate channel conditions between itself and each of receiving devices and, based on the evaluated channel quality information, determine a modulation and coding scheme for the group of receiving devices within its broadcast range.
Because a transmitting device may use a more robust MCS than is necessary for every receiving device in its range, receiving devices that could successfully receive data transmitted using a less robust MCS may unnecessarily expend resources decoding data transmitted using a more robust MCS. In addition, a receiving device may spend unnecessary resources to receive more copies or redundant bits of a PDU than is necessary to successfully decode the PDU.
The disclosed embodiments are directed to overcoming one or more of the problems set forth above.